In addition to killing 291 people and injuring hundreds, Wednesday's 6.2 magnitude quake flattened three medieval towns in central Italy

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Firefighters work outside the Hotel Roma in Amatrice, central Italy, Saturday, Aug. 27, 2016 where a 6.1 earthquake struck just after 3:30 a.m., Wednesday. As Italians observed a day of national mourning, President Sergio Mattarella and Premier Matteo Renzi joined grieving family members for a state funeral for some of the victims of Wednesday's quake.

Italian authorities are vowing to investigate whether negligence or fraud in adhering to building codes played a role in the high death toll in last week's earthquake in Italy.

They also called for efforts to ensure organized crime doesn't infiltrate lucrative construction contracts to eventually rebuild much of the picturesque towns leveled in the disaster.

Meanwhile, rescue workers pressed on with the task of recovering bodies from the rubble, with hopes of finding any more survivors virtually vanished four days after the powerful quake.

Over the past two days, they found six more bodies in the rubble of Hotel Roma in Amatrice, the medieval hill town in mountainous central Italy that bore the brunt of destruction and loss of life in the powerful quake. They recovered three and by late Sunday were still working to retrieve others that were hard to reach.

It wasn't clear if those six were included in the overall 290 death toll given by authorities. The Civil Protection agency, which combines the figures it receives from different provinces affected by the quake, said the number is lower than the previous toll of 291 dead due to a correction in the numbers from the province of Rieti, where most of the victims died.

The quake that struck before dawn Wednesday also injured nearly 400 people as it flattened three medieval towns near the rugged Apennines. Prosecutor Giuseppe Saieva, based in the nearby provincial capital of Rieti, said the high human death toll "cannot only be considered the work of fate."

"The fault lines tragically did their work and this is called destiny, but if the buildings had been built like in Japan they would not have collapsed," Saieva said in comments carried by Italian media.

Investigations are focusing on a number of structures, including an elementary school in Amatrice that crumbled despite being renovated in 2012 to resist earthquakes at a cost of 700,000 euros ($785,000). With schoolchildren's summer vacations in their final weeks, the school wasn't yet in use. Many were shocked that it didn't withstand the 6.2 magnitude quake.

After an entire first-grade class and a teacher were killed in a 2002 quake in the southern town of San Giuliano di Puglia, Italian officials had pledged citizens that safety of schools, hospitals and other critical public buildings would be guaranteed.

Questions also surround a bell tower in Accumoli that collapsed, killing a family of four sleeping in a neighboring house, including a baby of 8 months and a 7-year-old boy. That bell tower also had been recently restored with special funds allocated after Italy's last major earthquake, which struck nearby L'Aquila in 2009.

Italy's national anti-Mafia prosecutor, Franco Roberti, also vowed to work to prevent organized crime from infiltrating public works projects which will be eventually begun to rebuild the earthquake zone.

"This risk of infiltration is always high," he said in comments Sunday in La Repubblica newspaper. "Post-earthquake reconstruction is historically a tempting morsel for criminal groups and colluding business interests."

Deadly quakes that have led to criminal investigations of suspicions ranging from misuse of funds or corruption involving awarding of construction contracts include the 1980 temblor in the Naples area and a 2009 quake in L'Aquila, central Italy.

Roberti noted he wasn't involved in the local prosecutors' probes into last week's quake. But he added that if buildings are well-constructed according to regulations for earthquake-prone zones, "parts of buildings can be damaged and cracked but they don't pulverize and implode."

Italy's national museums, meanwhile, embarked on a fundraising campaign, donating their proceeds Sunday to relief and reconstruction efforts in the quake-stricken areas.

Besides homes and low-rise apartment buildings, Wednesday's quake badly damaged scores of churches, town halls, bell towers and other centuries-old cultural treasures. The idea is to use art for art — harnessing the nation's rich artistic heritage to help repair and restore other objects of beauty in the hard-hit towns.

"It's a way to rediscover our cultural heritage, to give our small but significant contribution so that endangered artwork that was gravely damaged may have a new chance, be restored and recovered," Cristiana Collu, the director of Rome's National Gallery of Modern and Contemporary Art Museum, said in an interview with The Associated Press.

Also Sunday, Pope Francis told faithful in St. Peter's Square he hopes to soon visit people in the quake-ravaged regions to bring them "the comfort of faith."

Amatrice bore the brunt of earthquake's destruction, with at least 229 fatalities and its medieval heart nearly obliterated. Eleven others died in nearby Accumoli and 50 more in Arquata del Tronto, 10 miles (16 kilometers) north of Amatrice.

On Saturday, a state funeral took place for 35 of the victims in the town of Ascoli Piceno, which escaped the heavy damage of other towns in the region. That funeral involved most of the dead from Arquata del Tronto. Some of the dead from Amatrice were still in the town's makeshift morgue. Identified bodies were being kept in refrigerated trucks in an airport hangar in Rieti, 65 kilometers (40 miles) away. On Tuesday, a memorial service — without the bodies — will be held for the dead of Amatrice on the town's outskirts.

The last survivor was extracted from rubble on Wednesday evening, and hopes have virtually vanished of finding any living in the ruins.

The number still missing is uncertain, due to the many visitors seeking a last taste of summer in the cool hill towns when the quake struck.

The quake left a few thousands of people without homes, with nearly 2,700 hosted in a total of 58 tent "towns" set up on the outskirts of the ravaged areas, or improvised shelters, like a gym with a basketball court in Amatrice. Countless more who fled damaged homes -- or even the ones without any heavy damage -- went to stay with relatives in Rome and other Italian cities.